A. Field of the Invention
The present invention relates to an automatic selfdraining backflow preventer.
B. Description of the Prior Art
Backflow preventers, vacuum breakers, and the like are typically used in fluid systems between a fluid source and a fluid conduit such as a hose for preventing backflow if a decrease of fluid pressure from the fluid source occurs. Such a backflow preventer is disclosed in the U.S. Pat. No. 3,850,190.
Typically, prior art backflow preventers prevent backflow at the outlet of the preventer leaving residual water within the housing of the device. Since the preventer may be installed upon a hydrant on the exterior of a building, this trapped residual water is susceptable to freezing at below freezing ambient temperatures thereby causing damage to the hydrant.
Existing regulations covering the installation of backflow prevention devices require the vacuum breaker to be permanently affixed to the sillcock or hydrant to prevent unauthorized removal. Because this permanent fixture cannot be removed, prior art backflow preventers employ manual means to open a relief port to atmosphere allowing residual water within the preventer to drain from the area immediately upstream of the backflow preventer closure member and downstream from the hydrant. This requires an extra procedure to be performed manually, often resulting in inadequate drainage of the device. Moreover, this procedure is often overlooked resulting in damage to the hydrant and backflow preventer.
In the alternative, some prior art hydrants normally installed in residential buildings employ a separate shut-off valve located at a heated area inside the building. Accordingly, the water may be shut off inside the building and the hydrant opened allowing water to drain. However, these prior art backflow preventers preclude the possibility of drainage of the hydrant unless some means is provided to open the preventer to atmosphere in a manner that will allow purging of the freeze prone water and yet not allow the introduction of contamination.